1. Field of the Invention
The present invention relates to a thin film magnetic memory device having a magnetic film and a communication function as well as a radio chip, a distribution management system and a manufacturing process management system each using the thin film magnetic memory device.
2. Description of the Related Art
Attention has been paid to an MRAM (Magnetic Random Access Memory) device serving as a memory capable of storing nonvolatile data with lower consumption power. The MRAM device is a memory which stores data in a nonvolatile manner using a plurality of thin film magnetic elements formed on a semiconductor integrated circuit and which can randomly access the respective thin film magnetic bodies.
In recent years, it is particularly made public that the performance of the MRAM device surprisingly advances by using a thin film magnetic body utilizing a magnetic tunnel junction (MTJ) as a memory cell. The MRAM device which includes memory cells having magnetic tunnel junctions is disclosed in technical documents such as xe2x80x9cA 10 ns Read and Write Non-Volatile Memory Array Using a Magnetic Tunnel Junction and FET Switch in each Cellxe2x80x9d, ISSCC Digest of Technical Papers, TA7.2, February 2000 and xe2x80x9cNonvolatile RAM based on Magnetic Tunnel Junction Elementsxe2x80x9d, ISSCC Digest of Technical Papers, TA7.3, February 2000.
FIG. 17 is a schematic diagram showing the configuration of a memory cell having a magnetic tunnel junction (which memory cell will be also referred to simply as xe2x80x9cMTJxe2x80x9d memory cell hereinafter).
Referring to FIG. 17, the MTJ memory cell includes a tunnel magneto-resistance element TMR having electric resistance changing according to the data level of magnetically written, stored data, and an access element ATR. Access transistor ATR is connected to tunnel magneto-resistance element TMR in series between a bit line BL and a source line SL. Access element ATR is typically formed out of a field effect transistor.
Bit line BL for carrying a data write current and a data read current during data write and data read, respectively, a write digit line WDL for carrying the data write current during data write, a word line WL for instructing data to be read, and source line SL for pulling down the voltage of tunnel magneto-resistance element TMR to a ground voltage GND during data read are arranged for the MTJ memory cell.
During data read, tunnel magneto-resistance element TMR is electrically connected between source line SL (ground voltage GND) and bit line BL when access transistor ATR is turned on.
FIG. 18 is a conceptual view for explaining a data write operation for writing data to the MTJ memory cell.
Referring to FIG. 18, tunnel magneto-resistance element TMR includes a magnetic body layer which has a fixed magnetization direction (which layer will be also simply referred to as xe2x80x9cfixed magnetic layerxe2x80x9d hereinafter) FL and a magnetic body layer which is magnetized in a direction according to a data write magnetic field generated by the data write current (which layer will be also simply referred to as xe2x80x9cfree magnetic layerxe2x80x9d hereinafter) VL. A tunneling barrier TB formed out of an insulating film is provided between fixed magnetic layer FL and free magnetic layer VL. Free magnetic layer VL is magnetized in the same direction as or the opposite direction to the magnetization direction of fixed magnetic layer FL in accordance with the level of written, stored data.
The electric resistance of tunnel magneto-resistance element TMR changes according to the relative relationship in magnetization direction between fixed magnetic layer FL and free magnetic layer VL. Specifically, if the magnetization layer of fixed magnetic layer FL is the same as (parallel to) that of free magnetic layer VL, the electric resistance of tunnel magneto-resistance element TMR becomes lower than that of tunnel magneto-resistance element TMR if the magnetization direction of fixed magnetic layer FL is opposite (anti-parallel) to that of free magnetization direction FL.
During data write, word line WL is inactivated and access transistor ATR is turned off. In this state, data write currents for magnetizing free magnetic layer VL are applied to bit line BL and write digit line WDL, respectively in accordance with the level of written data. That is, the magnetization direction of free magnetic layer VL is determined according to the directions of the data write currents carried to write digit line WDL and bit line BL, respectively.
FIG. 19 is a conceptual view showing the relationship between the data write current and the magnetization direction of the MTJ memory cell.
Referring to FIG. 19, the horizontal axis Hx indicates the direction of a magnetic field H(WDL) generated by the data write current carried to write digit line WDL. The vertical axis Hy indicates a magnetic field H(BL) generated by the data write current carried to bit line BL.
The magnetization direction of free magnetic layer VL is updated only if the sum of magnetic fields H(WDL) and H(BL) reaches an external region of an asteroid characteristic line shown. That is, to execute data write, it is necessary to carry a sufficient data write current to generate a magnetic field having an intensity exceeding a predetermined intensity to both of write digit line WDL and bit line BL.
On the other hand, if a magnetic field corresponding to the inner region of the asteroid characteristic line is applied, the magnetization direction of free magnetic layer VL has no changed. Namely, if a predetermined data write current is applied only to one of write digit line WDL and bit line BL, data write is not executed. The magnetization direction which has been written to the MTJ memory cell, i.e., stored data level is held in a nonvolatile manner until new data is written. As indicated by the asteroid characteristic line, it is possible to decrease a necessary magnetization threshold to change the magnetization direction along a magnetization easy axis by applying a magnetic field in a magnetization hard axis direction to free magnetic layer VL.
FIG. 20 is a conceptual view for explaining a data read operation for reading data from the MTJ memory cell.
Referring to FIG. 20, during data read, access transistor ATR is turned on in response to the activation of word line WL. As a result, tunnel magneto-resistance element TMR is electrically connected to bit line BL while being pulled down to ground voltage GND. In this state, by applying a data read current Is to a current path including bit line BL and tunnel magneto-resistance element TMR, voltage change according to the electric resistance of tunnel magneto-resistance element TMR, i.e., the level of the stored data of the MTJ memory cell can be generated in bit line BL. For example, if precharging bit line BL with a predetermined voltage and then starting the supply of data read current Is, it is possible to read the data stored in the MTJ memory cell by detecting the voltage of bit line BL.
FIG. 21 is a block diagram of an MTJ memory cell formed on a semiconductor substrate.
Referring to FIG. 21, access transistor ATR formed on a semiconductor substrate SUB includes source/drain regions 310 and 320 which are n-type regions, and a gate 330. Source/drain region 310 is electrically connected to source line SL through a metal film formed in a contact hole 341.
Write digit line WDL is formed on a metal wiring layer formed on the upper layer of source line SL. Tunnel magneto-resistance element TMR is electrically connected to source/drain region 320 of access transistor ATR through a metallic film formed on a strap 345 and a contact hole 340. Strap 345 is provided to electrically connect tunnel magneto-resistance element TMR to access transistor ATR and is formed out of a conductive material.
Bit line BL is electrically connected to tunnel magneto-resistance element TMR and provided on the upper layer of tunnel magneto-resistance element TMR. As already described, during data write, it is necessary to carry a data write current to each of bit line BL and write digit line WDL. During data read, if word line WL is activated to, for example, a high voltage state, access transistor ATR is turned on. As a result, tunnel magneto-resistance element TMR pulled down to ground voltage GND is electrically connected to bit line BL through access transistor ATR.
Bit line BL to which a data write current and a data read current is applied and write digit line WDL to which a data write current is applied are each formed using a metal wiring layer. On the other hand, word line WL is provided to control the gate voltage of access transistor ATR, so that it is unnecessary to actively carry a current to word line WL. Accordingly, from a viewpoint of enhancing integration, word line WL is normally formed on the same wiring layer as that of gate 330 by using a polysilicon layer, a polyside layer or the like without the need to newly provide an independent metal wiring layer.
FIG. 22 is a top view of the MTJ memory cell having a structure shown in FIG. 21.
Referring to FIG. 22, the MTJ memory cell is arranged to correspond to the intersection between word line WL and bit line BL arranged in a mesh. As shown in FIG. 21, tunnel magneto-resistance element TMR in each MTJ memory cell is connected to corresponding bit line BL through contact hole 342.
In the meantime, as a memory capable of reading and writing data in a non-contact manner, a so-called radio chip which has a radio communication function for communicating with the outside of the memory by a loop antenna or the like and a data storage function by the nonvolatile memory has been developed.
Japanese Patent Laying-Open No. 8-315247 discloses an article management method by employing such a radio chip as a data carrier. According to this article management method, management data on the manufacturing, sales, maintenance and the like of articles is written to the radio chip and the radio chip is included in each article or the like. That is, by reading stored data from the radio chip employed as a data carrier, writing additional data thereto or changing the data in an article distribution process, it is possible to efficiently conduct distribution, sales, examination, inspection and the like.
Further, as disclosed by Japanese Patent Laying-Open Nos. 2000-57282 and 2000-59260, a radio chip of this type can be also utilized as a so-called non-contact type IC card.
Normally, an EEPROM (electrically erasable programmable read only memory) or a flash EEPROM is employed as a nonvolatile memory included in such a radio chip. Each of these memories, however, requires relatively high voltage for a data rewrite operation and a data erasure operation. For that reason, it is undesirable to mount such a memory on a radio chip the internal generation power of which is limited. In other words, the development of a radio chip requiring lower consumption power is desired.
Furthermore, to enhance the communication capability of the radio chip, i.e., to increase a communicable distance, it is necessary to secure the inductance value of an antenna section. Due to this, according to a conventional radio chip, a communication capability and a chip size holds a trade-off relationship, making it difficult to provide a radio chip smaller in size. As a result, it is particularly difficult to apply a radio chip to a thin film target such as a paper product.
It is an object of the present invention to provide a thin film magnetic memory device which can be made small in size and reduce consumption power and which can establish non-contact data communication with the outside of the memory, as well as a radio chip, a distribution management system and a manufacturing process management system each using the thin film magnetic memory device.
In short, according to one aspect of the present invention, there is provided a thin film magnetic memory device formed on a substrate, including: a conductive wiring formed on the substrate; and a first magnetic film selectively formed on at least one of surfaces of the conductive wiring on the substrate to correspond to at least a portion right under the conductive wiring.
Therefore, the main advantage of the present invention is in that the inductance value of the conductive wiring can be increased by utilizing a magnetic film manufacturing step which is necessarily included in the steps of manufacturing the thin film magnetic memory device.
It is preferable that the thin film magnetic memory device further includes: a memory array section having a plurality of magnetic memory cells each having a second magnetic film for magnetically holding stored data, arranged therein; an array peripheral circuit section for reading and writing the stored data from and to the memory array section; an antenna section constituted out of the conductive wiring formed into the loop; and a peripheral circuit section for generating an operation instruction to the peripheral circuit section based on a radio wave received by the antenna section.
Therefore, the antenna section for communicating with the outside is constituted using the inductance wiring having an increased inductance value, whereby the antenna section which is formed small in size and thin can secure communication capability.
It is also preferable that the peripheral circuit section includes a power supply control section generating an operating power supply voltage of the thin film magnetic memory device using an induced current generated on the conductive wiring by the radio wave as a source.
Therefore, the operating power supply voltage can be secured by an induced current generated by the radio wave received by the antenna section. As a result, it is possible to semipermanently use the thin film magnetic memory device capable of operating with low consumption power without requiring high voltage unlike EEPROM or the like, without the need to consider the service life of a battery.
According to yet another aspect of the present invention, there is provided a distribution management system, including: a tag chip integrally embedded into a distributed article; a database section for collating and registering management data on the distributed article; a management data read device for reading the management data from the tag chip in a nonvolatile manner, and collating the read management data for the database section; and a management data write device wiring the management data from the tag chip in a nonvolatile manner, and collating the read management data for the database section. The tag chip includes a thin film magnetic memory device having a memory array section arranged therein a plurality of magnetic memory cells magnetically holding the management data. The thin film magnetic memory device includes: an array peripheral circuit section for reading and writing data from and to the memory array section; an antenna section constituted out of a conductive wiring having at least a lower surface covered with a magnetic film; a power supply control section for generating an operating power supply voltage of the tag chip using an induced current generated on the conductive wiring by a radio wave received by the antenna section as a source; and a transmission and receiving section for instructing the array peripheral circuit section to read and write the management data stored in the memory array section based on the radio wave received by the antenna section between the management data read device and the management data write device.
Such a distribution management system can manage distribution by non-contact transmission and receiving of management data using the thin film magnetic memory device including the small-sized antenna as a tag chip. By making the antenna smaller and thinner, in particular, it is possible to expand the range of distributed articles the distribution of which can be managed. Further, since the tag chip which uses the thin film magnetic memory device can be sufficiently supplied with operating power by an external radio wave, it is unnecessary to consider the service life of a battery.
According to still another aspect of the present invention, there is provided a manufacturing process management system including: an ID chip added to a semifinished article subjected to a plurality of predetermined manufacturing processes; and a process management device transmitting and receiving to and from the ID chip in a non-contact manner in each of the manufacturing processes. The ID chip includes a thin film magnetic memory device having a memory array section having arranged therein a plurality of memory cells magnetically holding the process management data. The thin film magnetic memory device includes: an array peripheral circuit section for reading and writing data from and to the memory array section; an antenna section constituted out of a conductive wiring having at least a lower surface covered with a magnetic film; a power supply control section generating an operating power supply voltage of the tag chip using an induced current generated on the conductive wiring by a radio wave received by the antenna section as a source; and a transmission and receiving section for instructing the array peripheral circuit section to read and write the management data stored in the memory array section based on the radio wave received by the antenna section between the management data read device and the management data write device.
Such a manufacturing process management system can manage the manufacturing processes by the non-contact transmission and receiving of management data using the thin film magnetic memory device including the small-sized antenna as an ID chip. By making the antenna thinner and smaller, in particular, it is possible to apply this manufacturing process management system to the manufacturing processes of a very small or thin film product. Furthermore, since the ID chip which uses the thin film magnetic memory device can be sufficiently supplied with operating power by an external radio wave, it is unnecessary to consider the service life of a battery.
Preferably, if the semifinished article has been subjected to all of the plurality of predetermined manufacturing processes, the ID chip is removed and the removed ID chip is added to another semifinished article after the process management data is reregistered.
Since process management data is reregistered in the ID chip removed from the finished article and the ID chip is added to another semifinished article, it is also possible to semipermanently, repeatedly use the ID chip.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.